The respiratory system brings in and the digestive system breaks down so that both substances are available to cells to make .

Oxygen; food; adenosine triphosphate (ATP).

Explanation:

Cellular respiration can be defined as a series of metabolic reactions that typically occur in cells, so as to produce energy in the form of adenosine triphosphate (ATP). During cellular respiration, high energy intermediates are created that can then be oxidized to make adenosine triphosphate (ATP).

All living organisms such as plants and animals require energy to function properly (life activities). The cell organelle where energy from nutrients are released is generally referred to as mitochondria. Animals and plants retrieve energy using mitochondria to do cellular respiration because they typically act like a digestive system by taking in nutrients, breaking them down and obtaining energy rich molecules for cell-life activities.

This ultimately implies that, mitochondria provides all the energy required in the cell by transforming energy forms through series of chemical reactions; breaking down of glucose into Adenosine Triphosphate (ATP) used for providing energy for cellular activities in the body of living organisms.

Generally, oxygen goes into the body of a living organism such as plants, humans and animals when they breathe (respiratory system) while glucose is absorbed by the body when they eat (digestive system).

Hence, the respiratory system brings in oxygen and the digestive system breaks down food so that both substances are available to cells to make adenosine triphosphate (ATP).